#define _GNU_SOURCE 1
#include<sys/types.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<assert.h>
#include<stdio.h>
#include<unistd.h>
#include<errno.h>
#include<string.h>
#include<fcntl.h>
#include<stdlib.h>
#include<poll.h>

#include<sys/poll.h>

#define USER_LIMIT 5
#define BUFFER_SIZE 64
#define FD_LIMIT 65535

typedef struct client_data
{
    struct sockaddr_in address;
    char *write_buf;
    char   buf[BUFFER_SIZE];
}client_data;

int setnonblocking(int fd)
{
    int old_option = fcntl(fd, F_GETFL);
    int new_option = old_option | O_NONBLOCK;
    fcntl(fd, F_SETFL, new_option);
    return old_option;
}

int main(int argc, char * argv[])
{
    if(argc <= 2)
    {
        printf("usage: %s ip_address port_number\n", basename(argv[0]));
        return 1;
    }

    const char *ip = argv[1];
    int port = atoi(argv[2]);
    int listenfd;
    int ret = 0;
    struct sockaddr_in address;
    client_data *users = NULL;

    bzero(&address, sizeof(address));
    address.sin_family = AF_INET;
    inet_pton(AF_INET, ip, &address.sin_addr);
    address.sin_port = htons(port);

    if((listenfd = socket(PF_INET, SOCK_STREAM, 0)) < 0)
    {
        perror("create socket error ...\n");
        exit(-1);
    }
    else
    {
        printf("create socket success ...\n");
    }

    if((ret = bind(listenfd, (struct sockaddr*)&address, sizeof(address))) < 0)
    {
        perror("bind socket error...\n");
        exit(-1);
    }
    else
    {
        printf("bind socket success ...");
    }

    if((ret = listen(listenfd, 5)) < 0)
    {
        perror("listen error ...\n");
    }
    else
    {
        printf("start listen...\n");
    }

    assert(ret != -1);

    if((users = (client_data*)malloc(sizeof(client_data) * FD_LIMIT)) == NULL)
    {
        perror("malloc client_data error..\n");
    }
    else
    {
        printf("malloc client_data success\n");
    }

    struct pollfd fds[USER_LIMIT];
    int user_counter = 0;
    for(int i = 1; i <= USER_LIMIT; ++i)
    {
        fds[i].fd = -1;
        fds[i].events = 0;
    }

    fds[0].fd = listenfd;
    fds[0].events = POLLIN|POLLERR;
    fds[0].revents = 0;

    while(1)
    {
        ret = poll(fds, user_counter + 1, -1);
        if(ret < 0) 
        {
            printf("poll failure");
            break;
        }

        for(int i = 0; i < user_counter + 1; ++1)
        {
            if((fds[i].fd == listenfd) && (fds[i].revents & POLLIN))
            {
                struct sockaddr_in client_address;
                socklen_t client_len = sizeof(client_address);

                int connfd = accept(listenfd, (struct sockaddr*)&client_address, &client_len);
                if(connfd < 0)
                {
                    printf("errno is %d\n",errno);
                    continue;
                }

                if(user_counter >= USER_LIMIT)
                {
                    const char *info = "too many users\n";
                    printf("%s", info);
                    send(connfd, info, strlen(info), 0);
                    close(connfd);
                    continue;
                }

                user_counter++;
                users[connfd].address = client_address;
                setnonblocking(connfd);
                fds[user_counter].fd = connfd;
                fds[user_counter].events = POLLIN|POLLERR|POLLHUP;
                printf("comes a new user, now have %d users.\n", user_counter);
            }
            else if(fds[i].revents & POLLERR)
            {
                printf("get an error from %d\n", fds[i].fd);
                char errors[100];
                memset(errors, '\0', 100);
                socklen_t length = sizeof(errors);
                if(getsockopt(fds[i].fd, SOL_SOCKET, SO_ERROR, &errors, &length) < 0)
                {
                    printf("get socketopt fail\n");
                }
                continue;
            }
            else if(fds[i].revents & POLLHUP)
            {
                users[fds[i].fd] = users[fds[user_counter].fd];
                close(fds[i].fd);
                fds[i] = fds[user_counter];
                i--;
                user_counter--;
                printf("a client left\n");
            }
            else if(fds[i].revents & POLLIN)
            {
                int connfd = fds[i].fd;
                memset(users[connfd].buf, '\0', BUFFER_SIZE);
                ret = recv(connfd, users[connfd].buf, BUFFER_SIZE -1, 0);
                printf("get %d bytes of client_data %s from %d\n",ret, users[connfd].buf,connfd);
                if(ret < 0)
                {
                    if(errno != EAGAIN)
                    {
                        close(connfd);
                        users[fds[i].fd] = users[fds[user_counter].fd];
                        fds[i] = fds[user_counter];
                        i--;
                        user_counter--;
                    }
                }
                else if(ret == 0)
                {
                    printf("code should not come to here\n");
                }
                else
                {
                    for(int j = 1; j <= user_counter; ++j)
                    {
                        if(fds[j].fd == connfd)
                        {
                            continue;
                        }
                        fds[j].events |= ~POLLIN;
                        fds[j].events |= POLLOUT;
                        users[fds[j].fd].write_buf = users[connfd].buf;
                    }
                }
            }
            else if(fds[i].revents & POLLOUT)
            {
                int connfd = fds[i].fd;
                if(!users[connfd].write_buf)
                {
                    continue;
                }

                ret = send(connfd,  users[connfd].write_buf, strlen(users[connfd].write_buf), 0);
                users[connfd].write_buf = NULL;
                fds[i].events |=  ~POLLOUT;
                fds[i].events |= POLLIN;
            }
        }
    }
    
    free(users);
    close(listenfd);
    return 0;
}